Metal silicides have been employed in a variety of silicon structures as a way of reducing contact resistance. For example, various metal silicides can be employed as low resistance contact regions between bipolar junction transistors (BJTs) and phase change memory (PCM) cells. The memory element of a conventional PCM cell includes a chalcogenide material that can switch states (e.g., between crystalline, semi-crystalline, amorphous, and semi-amorphous states) upon changes in temperature. A BJT can enable the changes in temperature by selectively supplying or stopping current to an electrode of the PCM cell. A metal silicide contact region at the interface of the BJT and the electrode can decrease electrical resistance between the BJT and the electrode, reducing voltage requirements and improving an ability to switch the states of the chalcogenide material.
An example of a metal silicide frequently used to form a low resistance contact region of a BJT is cobalt disilicide (CoSi2). CoSi2 advantageously exhibits relatively low electrical resistance (e.g., from about 16 micro-ohm-centimeters to about 18 micro-ohm-centimeters), generally does not form tightly bound compounds with common p-type and n-type dopants, and forms a smooth and fine grained silicide. However, overgrowth-related problems (e.g., increased electrical resistance, current leakage, etc.) caused by the deficiencies of conventional methods of forming CoSi2 contact regions have limited the formation of CoSi2 contact regions to silicon structures having relatively large critical dimensions, such as areas larger than about 3600 nm2.
It would, therefore, be desirable to have an improved method of forming a metal silicide region, such as a CoSi2 contact region, that facilitates the formation of the metal silicide region confined within the critical dimensions of a smaller silicon structure, such as within an area of less than or equal to about 3600 nm2. It would be further desirable for such a method to provide improved control of the uniformity of the metal silicide region formed.